Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $148.46   3.703%   $153.9575   $153.96   $153.95   $154.00  
  Purchase #2 $72.77   13.731%   $82.762   $82.76   $82.75   $82.80  
  Purchase #3 $242.75   8.865%   $264.2698   $264.27   $264.25   $264.30  
  Purchase #4 $27.78   7.604%   $29.8924   $29.89   $29.90   $29.90  
  Purchase #5 $141.83   10.699%   $157.0044   $157.00   $157.00   $157.00  
  Purchase #6 $9.26   11.290%   $10.3055   $10.31   $10.30   $10.30  
  Purchase #7 $196.59   11.215%   $218.6376   $218.64   $218.65   $218.60  
  7 purchase totals = $839.44       $916.8292   $916.83   $916.80   $916.90